The effort in the past year has been trying to ascertain the biological significance and implication concerning the radicals and quinones of benzo(a)pyrene obtained through metabolism and the damage of the reactive reduced oxygen species generated by this quinone in a cyclic manner. The research has been conducted in three directions. 1. The metabolism of benzo(a)pyrene by the isolated nuclei and nuclear membrane has been investigated. 2) The toxicity of the quinone to the cells and the breakage of the cellular DNA by the quinone and by radiation has been investigated. 3) Special efort has been made to develop a sensitive method for the detection of DNA-protein crosslink which should be an indicaton of the attack by the radicals.